简单的C#&PHP对称加解密

byte[] ctxbytes = System.Text.Encoding.UTF8.GetBytes(ctx);
        byte[] keybytes = System.Text.Encoding.UTF8.GetBytes(key);
        int ctxLen = ctxbytes.Length;
        int keyLen = keybytes.Length;
        byte[] tempbytes = new byte[ctxLen];
        int index = 0;
        for (int i = 0; i < ctxbytes.Length; i++)
        {
            if (index == keyLen)
            {
                index = 0;
            }
            tempbytes[i] = (byte)(ctxbytes[i] ^ keybytes[index]);
            index++;
        }
        return System.Text.Encoding.UTF8.GetString(tempbytes, 0, tempbytes.Length);

$temp = "";
    $ctxLen = strlen($ctx);
    $keyLen = strlen($key);
    $index = 0;
    for ($i=0;$i<$ctxLen;$i++) {
        if ($index == $keyLen) {
            $index = 0;
        }
        $temp .= $ctx[$i] ^ $key[$index];
        $index++;
    }
    return $temp;